Re: [PATCH 1/2] usb: chipidea: Reduce ULPI PHY reset pulse to datasheet spec of 1us
From: Mike Looijmans
Date: Mon Jul 06 2015 - 08:54:39 EST
On 02-07-15 11:39, David Laight wrote:
From: Peter Chen
Sent: 30 June 2015 03:06
On Fri, Jun 26, 2015 at 03:47:03PM +0200, Mike Looijmans wrote:
The datasheet for the 334x PHY mentions that a reset can be performed:
"... by bringing the pin low for a minimum of 1 microsecond and
then high."
A delay of 5ms to implement that seems overly long, so reduce it to
just 1us.
As for the delay after reset, the datasheet only mentioned that the
chip will assert the DIR output. 1ms seems like a safe time to wait
for that to happen, so no change there.
Signed-off-by: Mike Looijmans <mike.looijmans@xxxxxxxx>
---
drivers/usb/chipidea/core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/usb/chipidea/core.c b/drivers/usb/chipidea/core.c
index e970863..c865abe 100644
--- a/drivers/usb/chipidea/core.c
+++ b/drivers/usb/chipidea/core.c
@@ -664,7 +664,7 @@ static int ci_hdrc_create_ulpi_phy(struct device *dev, struct ci_hdrc *ci)
dev_err(dev, "Failed to request ULPI reset gpio: %d\n", ret);
return ret;
}
- msleep(5);
+ udelay(1);
If the spec says 1us I'd delay for longer just to make sure.
And add a comment saying that the reset needs to be 1us long.
Why? It's not as if the chip would reset any "better" if you pull the line
longer. For some of these USB PHYs, the internal regulators and other analog
parts will be disabled as well and the longer you keep it in reset, the longer
it will take the device to start back up again.
The 1us value already takes into account a generous compensation for
temperature and other factors, and probably the reset will work just fine even
if you only use half the time.
Even if I'd agree with you here, I think you'll also have to admit that 5000x
the value in the datasheet might be a bit over the top.
M.
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